1. Field of the Invention
The present invention relates to an all-solid-state reflection-controllable electrochromic device using a magnesium-nickel based alloy thin film, and more particularly, to a novel all-solid-state reflection-controllable electrochromic device capable of electrically controlling the transmission of sunlight entering through window glass by reversibly and electrically changing the glass surface from a mirror state to a transparent state, a production process thereof, and a reflection-controllable member.
The present invention relates to an electrochromic device which has high transmittance when transparent and is capable of switching the state of the glass surface in a short period of time over a large surface area by employing a specific multilayer structure which uses a magnesium-nickel alloy thin film for a reflection-controllable layer. The present invention provides a novel all-solid-state reflection-controllable electrochromic device preferably used in window glass of buildings and automobiles to reduce the sensation of heat in a building or automobile by controlling the transmission of sunlight, for example, a reflection-controllable member incorporating said electrochromic device, and new technologies and new products relating to said reflection-controllable member.
2. Description of the Related Art
Generally, in buildings, window glass typically serves as a large passageway for the transfer of heat. For example, the proportion of heat lost through windows when heating a building during the winter may reach about 48%, while the proportion of heat that enters through windows when cooling during the summer may reach as much as about 71%. The same phenomenon applies to automobiles in which window glass also serves as a large passageway for the transfer of heat. In automobiles, the ratio of window glass to interior space is even larger than in buildings, leaving little room for persons inside to avoid the radiant heat. Consequently, the interior of an automobile located in a hot weather environment reaches an extremely high temperature.
In examples of measuring automobile interior temperatures in a summer environment in Japan, the air temperature inside a parked automobile has been found to reach nearly 70° C. In addition, with respect to the temperatures of interior parts and materials inside an automobile, the top of the instrument panel may reach nearly 100° C., while the roof may reach nearly 70° C. It goes without saying that riding in an automobile under such conditions is extremely uncomfortable. In addition, since the temperature of interior parts and materials does not readily lower even if the interior is ventilated or the air-conditioner is used, passengers continue to be radiated with radiant heat for a long period of time, thereby significantly decreasing the level of comfort within the vehicle.
Light-controllable glass has been developed as a technology for solving these problems which is capable of controlling the transfer of light and heat. There are several types of light-control systems used in light-controllable glass. Examples of light-controllable devices include: 1) electrochromic devices using a material which reversibly changes optical transmission by applying a current or voltage, 2) thermochromic devices using a material which changes transmission according to temperature, and 3) gas chromic devices using a material which changes transmission by controlling an atmospheric gas.
Among these, electrochromic devices are able to electrically control the transmission of light and heat. Consequently, electrochromic devices enable the transmission of light and heat to be set as desired, and are extremely suitable as light-controllable materials applied to building and automobile glass. Moreover, since these devices maintain the same optical characteristics when a current or voltage is not applied, the energy required to maintain a constant state of the devices can be reduced.
Although some compositions of electrochromic devices are in a liquid state, it is necessary to prevent leakage of liquid in such cases. Since buildings and automobiles are premised on long-term use, although it is possible to prevent leakage of liquid for a long period of time, this leads to higher costs. Consequently, all of the materials which compose electrochromic devices suitable for building and automobile glass are preferably solids in the manner of tungsten oxide.
Tungsten oxide and others known as electrochromic devices are based on the principle of controlling light by absorbing light with a light-controllable material. Namely, these devices control the entrance of heat in the form of light into an interior by absorbing light. However, in the case of employing a light-controllable material having this type of light-control principle, there is the problem of the light-controllable material retaining heat as a result of absorbing light, that heat being re-radiated into the interior, and that heat ending up penetrating into a light-controllable glass.
A technique for solving this problem has been proposed in which light is controlled by reflecting light instead of absorbing light. In other words, the entrance of heat into an interior caused by absorption of heat by a light-controllable material can be prevented by using a reflection-controllable material which reversibly changes between a mirrored state and a transparent state.
As an example of a reflection-controllable electrochromic devices having this characteristic, an electrochromic device having a reflection-controllable layers composed of an alloy of a rare earth metal and magnesium and a hydride thereof, a proton-conductive, transparent, oxidation protective layer, an anhydrous solid electrolyte layer and an ion storage layer being laminated therein (see Japanese Patent Application Laid-open No. 2000-204862).
The reflection-controllable layer has a function which controls optical reflectance of the electrochromic device, and reflectance changes due to the transfer of protons. The oxidation protective layer is composed of a compound having proton conductivity, examples of which include oxides such as niobium oxide, vanadium oxide and tantalum oxide, and fluorides such as magnesium fluoride and lead fluoride, and prevents oxidation of the reflection-controllable layer.
The ion storage layer accumulates protons used to control reflectivity. When a voltage is applied to a light-controllable glass, protons move from the ion storage layer into the reflection-controllable layer through solid electrolyte and oxidation protective layers, resulting in a change in the reflectance of the reflection-controllable layer. When a voltage is applied in the opposite direction thereto, protons are released from the reflection-controllable layer, and reflectivity of the reflection-controllable layer returns to its original level. In this device, however, since expensive rare earth metal is used for the reflection-controllable layer, applications to large surface areas are difficult from the viewpoint of cost.
As an example of another reflection-controllable device using a more practical material for the reflection-controllable layer, a device in which Mg2Ni is laminated for the reflection-controllable layer while palladium or platinum is laminated as a catalyst layer has been proposed (see U.S. Pat. No. 6,647,166). However, this type of material was unable to be used practically due to the low transmittance when the device is transparent.
A magnesium-nickel alloy thin film developed by some of the inventors of the present invention (see Japanese Patent Application Laid-open No. 2003-335553) is of the gas chromic type using hydrogen gas, and the visible light transmittance thereof is about 50%, which is considerably better than the level of 20% of previously reported Mg2Ni, and is close to practical application. As an example of an all-solid-state light-controllable mirror device using this magnesium-nickel alloy thin film, an all-solid-state light-controllable mirror optical switch has been proposed comprising an ion storage layer, a solid electrolyte layer and the magnesium-nickel alloy described in the above-mentioned Japanese Patent Application laminated in the form of a reflection-controllable device (see Japanese Patent Application Laid-open No. 2005-274630).
However, although the switching time of this device has a short when it changes from a reflecting state to a transparent state in the vicinity of an electrode, it has the problem of that the switching time becomes considerably longer as the distance increases from the electrode, thereby preventing its use in windows and so forth. Consequently, there has been a strong desire in the relevant technical field for the development of an all-solid-state reflection-controllable electrochromic device having high transmittance when transparent, and capable of switching over a large surface area.